<?php
/**
 * CDummyCache class file.
 *
 * @author Qiang Xue <qiang.xue@gmail.com>
 * @link http://www.yiiframework.com/
 * @copyright 2008-2013 Yii Software LLC
 * @license http://www.yiiframework.com/license/
 */

/**
 * CDummyCache is a placeholder cache component.
 *
 * CDummyCache does not cache anything. It is provided so that one can always configure
 * a 'cache' application component and he does not need to check if Yii::app()->cache is null or not.
 * By replacing CDummyCache with some other cache component, one can quickly switch from
 * non-caching mode to caching mode.
 *
 * @author Qiang Xue <qiang.xue@gmail.com>
 * @package system.caching
 * @since 1.0
 */
class CDummyCache extends CApplicationComponent implements ICache, ArrayAccess
{
    /**
     * @var string a string prefixed to every cache key so that it is unique. Defaults to {@link CApplication::getId() application ID}.
     */
    public $keyPrefix;

    /**
     * Initializes the application component.
     * This method overrides the parent implementation by setting default cache key prefix.
     */
    public function init()
    {
        parent::init();
        if ($this->keyPrefix === null)
            $this->keyPrefix = Yii::app()->getId();
    }

    /**
     * Retrieves a value from cache with a specified key.
     * @param string $id a key identifying the cached value
     * @return mixed the value stored in cache, false if the value is not in the cache, expired or the dependency has changed.
     */
    public function get($id)
    {
        return false;
    }

    /**
     * Retrieves multiple values from cache with the specified keys.
     * Some caches (such as memcache, apc) allow retrieving multiple cached values at one time,
     * which may improve the performance since it reduces the communication cost.
     * In case a cache doesn't support this feature natively, it will be simulated by this method.
     * @param array $ids list of keys identifying the cached values
     * @return array list of cached values corresponding to the specified keys. The array
     * is returned in terms of (key,value) pairs.
     * If a value is not cached or expired, the corresponding array value will be false.
     */
    public function mget($ids)
    {
        $results = array();
        foreach ($ids as $id)
            $results[$id] = false;
        return $results;
    }

    /**
     * Stores a value identified by a key into cache.
     * If the cache already contains such a key, the existing value and
     * expiration time will be replaced with the new ones.
     *
     * @param string $id the key identifying the value to be cached
     * @param mixed $value the value to be cached
     * @param integer $expire the number of seconds in which the cached value will expire. 0 means never expire.
     * @param ICacheDependency $dependency dependency of the cached item. If the dependency changes, the item is labeled invalid.
     * @return boolean true if the value is successfully stored into cache, false otherwise
     */
    public function set($id, $value, $expire = 0, $dependency = null)
    {
        return true;
    }

    /**
     * Stores a value identified by a key into cache if the cache does not contain this key.
     * Nothing will be done if the cache already contains the key.
     * @param string $id the key identifying the value to be cached
     * @param mixed $value the value to be cached
     * @param integer $expire the number of seconds in which the cached value will expire. 0 means never expire.
     * @param ICacheDependency $dependency dependency of the cached item. If the dependency changes, the item is labeled invalid.
     * @return boolean true if the value is successfully stored into cache, false otherwise
     */
    public function add($id, $value, $expire = 0, $dependency = null)
    {
        return true;
    }

    /**
     * Deletes a value with the specified key from cache
     * @param string $id the key of the value to be deleted
     * @return boolean if no error happens during deletion
     */
    public function delete($id)
    {
        return true;
    }

    /**
     * Deletes all values from cache.
     * Be careful of performing this operation if the cache is shared by multiple applications.
     * @return boolean whether the flush operation was successful.
     * @throws CException if this method is not overridden by child classes
     */
    public function flush()
    {
        return true;
    }

    /**
     * Returns whether there is a cache entry with a specified key.
     * This method is required by the interface ArrayAccess.
     * @param string $id a key identifying the cached value
     * @return boolean
     */
    public function offsetExists($id)
    {
        return false;
    }

    /**
     * Retrieves the value from cache with a specified key.
     * This method is required by the interface ArrayAccess.
     * @param string $id a key identifying the cached value
     * @return mixed the value stored in cache, false if the value is not in the cache or expired.
     */
    public function offsetGet($id)
    {
        return false;
    }

    /**
     * Stores the value identified by a key into cache.
     * If the cache already contains such a key, the existing value will be
     * replaced with the new ones. To add expiration and dependencies, use the set() method.
     * This method is required by the interface ArrayAccess.
     * @param string $id the key identifying the value to be cached
     * @param mixed $value the value to be cached
     */
    public function offsetSet($id, $value)
    {
    }

    /**
     * Deletes the value with the specified key from cache
     * This method is required by the interface ArrayAccess.
     * @param string $id the key of the value to be deleted
     * @return boolean if no error happens during deletion
     */
    public function offsetUnset($id)
    {
    }
}
